Various types of so-called adhesive tape-like medical adhesive sheets comprising a support such as a nonwoven sheet, a plastic film or the like having formed on one surface thereof a pressure-sensitive adhesive layer have been proposed as dressings for protection of the affected part of the skin or for administration of a drug for treating a disease or for prevention through a skin surface.
It is required for those medical adhesive sheets to have adhesiveness to the skin to some extent to prevent the same from falling off the skin surface to which the sheet is applied. However, physical irritation increases in peeling and removing the sheet from the skin surface as the adhesiveness to the skin increases, and pain or peeling of stratum corneum tends to occur. As a result, there is the possibility to give unnecessary irritation or damage to the skin surface, thereby giving pain to the user.
It is therefore necessary to appropriately decrease the adhesiveness to the skin in relationship with decrease of the skin irritation, and the adhesiveness to the skin is sacrificed to a certain degree, or the insufficient adhesiveness to the skin is supplemented by covering with a separately prepared adhesive sheet.
The medical adhesive sheet is also required to have, besides the appropriate adhesiveness, cohesiveness of the adhesive layer and an anchoring property of the adhesive layer to the support for preventing the adhesive from remaining on the skin on removal (adhesive remaining phenomenon). In particular, where the adhesive layer contains a drug for percutaneous absorption, the drug should have stability with time (insusceptibility to decomposition) in the adhesive layer and releasability from that layer (percutaneous absorbability). Thus, development of medical adhesive sheets must be undertaken with due consideration for these various factors.
The present inventors had been devoted to develop a low-irritating medical adhesive sheet, especially an adhesive sheet having an adhesive layer comprising an acrylic polymer, which has hitherto been used as an adhesive less irritating to the skin, endowed with increased softness by incorporating a relatively large amount of an organic liquid component having a plasticizing action. As a result, they succeeded to obtain an adhesive layer with good balance between skin adhesion and low skin irritation. However, where the support, on which such an adhesive layer is laminated, is a mere plastic film or a composite film composed of a plastic film and a porous film, cases are sometimes met with, in which the proportions of the components constituting the adhesive layer vary and, in particular, the organic liquid component in the adhesive layer blooms to the interface between the support and the adhesive layer, failing to exert sufficient anchoring force. Such being the case, it turned out that anchoring failure tends to occur on removal from the skin after use, allowing the adhesive to remain on the skin. Improvement on anchoring property in medical adhesive sheets is of extreme importance to be considered in the development of medical adhesive sheets, although little study has ever been directed thereto.